Nerve-responsive troponin I slow promoter does not respond to unloading.
We examined the regulation of the troponin I slow (TnIs) promoter during skeletal muscle unloading-induced protein isoform transition, by using a transgenic mouse line harboring the -4,200 to +12 base pairs region of the human TnIs promoter. Eighteen female transgenic mice ( approximately 30 g body mass) were randomly divided into two groups: weight-bearing (WB) controls (n = 9) and hindlimb unloaded (HU; n = 9). The HU mice were tail suspended for 7 days. Body mass was unchanged in the WB group but was reduced (-6%; P < 0.05) after the HU treatment. Absolute soleus muscle mass (-25%) and soleus mass relative to body mass (-16%) were both lower (P < 0.05) in the HU group compared with the WB mice. Northern blot analyses indicate that 7 days of HU result in a 64% decrease (P < 0.05) in the abundance of endogenous TnIs mRNA (microg/mg muscle) in the mouse soleus. Furthermore, there is a trend for the abundance of the fast troponin I mRNA to be increased (+34%). Analysis of transgenic chloramphenicol acetyltransferase activity in the soleus muscle revealed no difference (P > 0.05) between WB and HU groups. We conclude that additional elements are necessary for the TnIs gene to respond to an unloading-induced, slow-to-fast isoform transition stimulus.
Criswell
D S
DS
Department of Integrative Biology, Pharmacology, and Physiology, University of Texas Medical School, Houston, Texas 77030, USA.
Hodgson
V R
VR
Hardeman
E C
EC
Booth
F W
FW
D000818:Animals; D015152:Blotting, Northern; D001835:Body Weight / Q000502:physiology; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D015342:DNA Probes; D005260:Female; D019417:Hindlimb Suspension / Q000502:physiology*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000201:enzymology / Q000502:physiology*; D009929:Organ Size / Q000502:physiology; D012313:RNA / Q000096:biosynthesis; D014158:Transcription, Genetic; D019210:Troponin I / Q000235:genetics / Q000502:physiology*
D015342:DNA Probes; D019210:Troponin I; D012313:RNA; D015500:Chloramphenicol O-Acetyltransferase